The subject matter of the present invention relates to a method and apparatus for isolating a first section of a wellbore from a second section of the wellbore which is disposed below the first section and adjacent a formation penetrated by the wellbore in order that a wellbore tool string of any desired length may be made up in the first section prior to opening a ball valve, and lowering the tool string downhole into the second section of the wellbore for performing one or more wellbore operations downhole in the second section.
When performing wellbore operations downhole, it is necessary to first make up a tool string at the surface of the wellbore prior to lowering that tool string downhole for performing the wellbore operations. In the past, the length of the tool string was limited and a longer tool string length was often desired. Therefore, when the tool string performed the wellbore operations downhole, that tool string was raised uphole and another, second tool string was made up at the surface of the wellbore. The second tool string was lowered downhole for performing additional wellbore operations. However, it is time consuming and expensive to continually make up additional tool strings at the wellbore surface, following the performance of the initial wellbore operation by the first tool string, and sequentially lower those additional tool strings downhole for performing additional wellbore operations. It would be desirable to make up one tool string having the desired length at the wellbore surface and to lower that desired tool string downhole for performing a wellbore operation during one trip into the wellbore. For example, when the tool strings include perforating guns, in the past, it was necessary to implement the following perforating procedure when perforating long length intervals of a wellbore: perforate the long length interval during multiple trips into the wellbore by making up, at the wellbore surface, a first perforating gun having a limited first length, lowering the first perforating gun downhole, perforating a formation penetrated by the wellbore, raising the first perforating gun uphole (or dropping that perforating gun to the bottom of the wellbore), making up a second perforating gun having another second limited length at the wellbore surface, lowering the second perforating gun downhole, perforating another section of the formation, raising the second perforating gun uphole (or dropping it to a bottom of the wellbore), etc. The above referenced perforating procedure is time consuming and costly.
As a result, it became necessary to design a method and apparatus for creating a tool string, of any desired length, uphole at the surface of the wellbore, so that the tool string may be lowered downhole and wellbore operations performed downhole during only one trip into the wellbore. U.S. Pat. 5,509,481 to Huber et al discussed one method for perforating long length intervals of a formation during a single run into the wellbore. The Huber apparatus disclosed an automatic release apparatus which would disconnect one part of a long gun string from a second part of the gun string just before the perforating guns of that gun string would detonate.
Another prior pending application also discloses a method and apparatus for making up, at the wellbore surface, a tool string of any desired length prior to lowering that tool string downhole for performing a wellbore operation in the wellbore during one trip into the wellbore. In a prior pending application entitled "Completions Insertion and Retrieval Under Pressure (CIRP) Apparatus including the Snaplock Connector", filed on Apr. 25, 1996, corresponding to attorney docket number 22.1183, and corresponding to a prior filed provisional application Ser. No. 60/010,500 filed Jan. 24, 1996 (hereinafter, the "CIRP application"), a tool string of any desired length is built uphole prior to lowering that tool string downhole by first holding a first tool, having a first and a second section of a snaplock connector connected thereto, in a deployment BOP or snaplock operator while suspending a second tool, also having a third section of the snaplock connector connected thereto, by wireline in a lubricator. The second tool is lowered down through the lubricator and through a master valve by operating a winch until the third section of the snaplock connector on the second tool connects to the second section of the snaplock connector on the first tool thereby forming a first tool string having a length which corresponds to the first tool and the second tool. The hold by the deployment BOP is released from the first tool, the first tool string is lowered, and the deployment BOP grips the second tool. The second tool also includes another first, second, and third section of a snaplock connector connected to its opposite side, the third section (called a deployment stinger) being connected to the wireline. The deployment stinger is raised uphole by operating the winch, and it is replaced by a third tool, such as a firing head, which also includes a third section of a snaplock connector. The third tool suspends by the wireline in the lubricator and it is lowered downhole and attached to the second tool being held by the deployment BOP. The hold by the deployment BOP on the second tool is released, and a resultant tool string of the desired length, consisting of the first tool, the second tool, and the third tool, is lowered downhole for the purpose of performing wellbore operations downhole during one trip into the wellbore.
However, another alternate apparatus, and corresponding method, is needed for isolating the formation downhole by means of closing a valve so that wellhead pressure can be bled off for building a long tool string uphole of any desired length and lowering that tool string downhole without a need for snubbing under wellhead pressure for the purpose of performing wellbore operations downhole during a single trip into the wellbore.